Day Two: Assembling the Galileoscope

Getting Ready
Before class, you should assemble a Galileoscope on your own and be comfortable with all the procedures. There are several small parts and you may want to consider how to help the students keep track of them. If you are going to have the students assemble the Galilean eyepiece and Barlow on day three, you should make arrangements on how to store the Galileoscopes and the pieces overnight where they will not get lost.

You do not want students to get fingerprints on the lenses. The main lens is wrapped in tissue paper. You may have the students handle the lenses with the tissue paper to avoid getting them dirty. Another option is to buy gloves for students to wear while handling the lenses. We have used rubber gloves (such as cleaning gloves). Photo shops sometimes sell cotton gloves that are used by professional photographers. Cotton gloves are more expensive, however (between $1-$2 per pair).

Teachers of young students may find the eyepiece assembly is too complicated. In very young classes, teachers have pre-assembled the eyepieces and let the students assemble the rest of the telescope.

In Class
Divide the students into an appropriate number of groups depending on how many Galileoscopes and students you have. Emphasize to the students that they should NOT work ahead and do not remove parts from the box until they are instructed to do so. Make sure they know not to throw away packing material until they are told to do so (the eyepiece lenses are inside a small piece of packing material that is easy to accidentally throw away).

You can use the Galileoscope Assembly Powerpoint (link to Powerpoint) to lead your students through the assemble process. Have patience as the students are doing this for the first time.

Once you have the Plossl eyepiece assembled, you should have the students look through the telescope and practice focusing. Telescopes have what is called a near focus point. You cannot focus on objects closer to the telescopes than the near focus point. For the Galileoscope, the near focus point is about 20 feet. If students try to focus on objects closer than 20 feet, the image will always be blurry. Make sure students are focusing on objects at least 20 feet away. The far focus point of the Galileoscope is infinity so you can focus on objects as far away as you can see!

They will notice the image is upside down. Upside down images are common in astronomical telescopes. Making an upright image would require additional lenses. Each additional lens absorbs a little bit of light. Since astronomers observe faint objects, they want to lose as little light as possible and deal with upside down images.

To aim the Galileoscope, there is a bore site on the top of the tube. The site has a V- shape at the front of the tube and a point at the back of the tube. Line the tube up so the point fills in the V. The telescope will be pointing at the object covered by the site.

There are several times you should check the students’ work. Some of the more common mistakes in assembling the Galileoscope are

Inserting the objective lens backwards

Inserting the nut incorrectly into the slot (a point MUST be up!)

Not aligning the tongue and groove on the focuser tube

Using the large O-rings (instead of the small O-rings) to assemble the focuser tube

Inserting the eyepiece lenses incorrectly

Placing a small ring (instead of the large ring) on the outside of the main eyepiece

NOAO is the national center for ground-based nighttime astronomy in the United States and is operated by the Association of Universities for Research in Astronomy (AURA). under cooperative agreement with the National Science Foundation.